In truth, you almost would have to write a book to fully answer your question, but the fact that you even asked it means you are headed in the right direction. I came from being classically trained, and (mostly hating it) apply my classical theory to gospel and tweaking it to understand how gospel works. Now, to talk a little about what others are doing. The truth? Some of them really don't know, and therefore can't tell you, they just do it. If you find one who does, corner them kidnap them and hold them hostage until they give you their secret. Now me, I usually play some type of progression that has a theoritcal foundation. I have not just thrown chords together and pray they fit. I may do that someday to experiment. I really can not fully explain to you in a post what is going on, but personal message me your phone number if you are comfortable giving that out, and we can talk a little about it to get you started in the right direction.
